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v3.19.1

Subsequent Event (Details) - Definitive agreement with Jet airline company limited - aircraft |  |  | 12 Months Ended
--- | --- | --- | ---
Jan. 08, 2019 | Dec. 14, 2018 | Dec. 31, 2018
Subsequent events |  |  |
Number of aircrafts |  | 10 |
Number of aircrafts where sale and leaseback completed |  |  | 6
Subsequent event |  |  |
Subsequent events |  |  |
Number of aircrafts where sale and leaseback completed | 4 |  |

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- Definition Number of aircraft operated by the carrier. + References No definition available. + Details
Name: | us-gaap_NumberOfAircraftOperated
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Represents the number of aircrafts for which sale and leaseback transaction is completed. + References No definition available. + Details
Name: | wlfc_NumberOfAircraftSoldAndLeasedBack
Namespace Prefix: | wlfc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_TypeOfArrangementAxis=wlfc_DefinitiveAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |